“All right, let’s do it,” Churchill says, stepping behind the line of fire.

“One, two, three, four, five, six, seven,” junior Paul Salem counts before locking his air gun into a rifle stand. Then, with all the ease of the U.S. Marine Corps sniper he once was, he fires.

The BB pellet flies through a chronometer set up on a lab table to measure its speed. In a flash, it lodges in a big brick of ballistics gelatin Salem had mixed for the occasion and floats suspended like a tiny copper pearl in bleached amber.

“That’s good, that’s very good,” Churchill says, hustling over to the block with Salem and another student, junior Kelly Ostrofsky, who is assisting Salem with the experiments. Ostrofsky records how deep the pellet penetrated.

The firing is the first stage of a small experiment that may help answer a very big question. Churchill, the only paleontologist at Duke studying human evolution, wants to estimate more precisely the time when Stone Age people started using projectile weapons—most likely, mini spears flung using handmade throwers. Their innovation freed humans from the limitations of an earlier technology, heavier handheld thrusting spears, which could be thrown but not that far or with much force.

To Churchill, weapons are about much more in human history than hunting game or waging war. They are the tools that were pivotal to the success of our species at colonizing an entire planet over a surprisingly brief time. Weapons helped transform people into dominant predators wherever they settled and protected them from dangerous carnivores such as lions and leopards. They even gave them an edge against their rivals (and close cousins), the Neanderthals. Perhaps most important, projectile weapons produced enough stability to allow people to live in larger bands, forge more cooperation within groups, and create more specialization—the sort of stuff that makes the best of civilization possible, then and now.

With no peephole into the past, Churchill pursues how and when prehistoric people expanded their arsenals by studying fossils and surviving stone points for clues. When they don’t explain enough, he experiments with proxies. Hence the air gun, the ballistics gel, and those BB pellets.

“We appreciate Steve because he is a big-picture guy,” says Anne Pusey, chair of Duke’s evolutionary anthropology department, where Churchill is based. But as anyone who has tried to fill in blanks in big pictures knows, the work takes an awfully long time. And progress doesn’t always follow a straight line.

Weapons watch: ballistics gelatin

Chris Hildreth

As a kid growing up in northern Virginia, Churchill, who is fifty-one, imagined becoming a paleontologist. He liked the idea of finding and studying fossils to try to piece together what life was like in the deep past. But he pictured himself studying grade-school favorites: dinosaurs such as Tyrannosaurus rex or Triceratops, animals that went extinct 65 million years ago. “I didn’t think humans were that interesting,” he recalls.

At Virginia Polytechnic Institute and State University, where he enrolled in 1977, Churchill changed his mind. In the anthropology classes he took, teachers were excited about the fossil remains of a hominid named Lucy, which had been discovered only three years earlier in Africa, the cradle of human development. Lucy was, at the time, the oldest known member of our evolutionary clan, dating to 3.2 million years ago. (Older traces of our earliest human-like or “hominid” lineage, fossilized skeletal remains that paleontologists nicknamed Ardi, were reported in the scientific literature in 2009.)

By studying fossils such as Lucy (and now Ardi)—as well as clues embedded in our DNA—scientists have concluded that humans and chimpanzees, our closest living relatives, branched off from a common ancestor 5 to 7 million years ago. Churchill entered graduate school at the University of New Mexico eager to learn more.

In Albuquerque, Churchill studied with Erik Trinkaus, a researcher known widely in paleontological circles for his studies of Neanderthals (pronounced nee-AN-der-tals). Our closest human ancestors, Neanderthals emerged in Europe and the Near East but went extinct about 28,000 years ago. In the 1970s, a lot of scientists focused solely on Neanderthals’ possible kinship to modern Europeans. Trinkaus, the first to conclude that Neanderthals walked upright just as Homo sapiens do, instead encouraged his students to concentrate on how Neanderthals adapted to their very specific environments. That’s an approach Churchill adheres to today when studying all prehistoric hominids.

Most scientists studying ancient peoples have to work with a cast of the fossil or relic. But Trinkaus had an actual Neanderthal fossil in his laboratory: one of the skeletons recovered from Shanidar Cave in Iraq in the 1950s, on loan from the Smithsonian Institution. When graduate students worked in the lab into the night, Churchill recalls, they would sometimes take out the fossil—carefully—to get a good look. “You’d be holding a fossilized bone from a person who lived 75,000 years ago, and it was a real Neanderthal,” he says. “Yes, there was a certain coolness.”

But he got a much bigger charge during his second year in Albuquerque. An archaeology professor invited him to look at some Neanderthal stone tools that had been discovered in the Dordogne region of France. The professor was rifling through a drawer for a particular object to show Churchill and pulled out what archaeologists call a scraper tool. It was a milky-white piece of flint that a Neanderthal had shaped in just the right way so it would have a sharp edge and a good grip. It was probably used to scrape animal hides or strip branches.

“He said, ‘Hold this,’ ” Churchill says, clearly still stirred by the memory. “It fit so well in my hand. Not only did a Neanderthal make it, a Neanderthal used it. When you hold a tool, you are interacting with their behavior in a way you are not when holding a bone.”

To this day, Churchill makes a point of passing around a hand ax made by a much older hominid, Homo erectus, when he teaches his human evolution class at Duke. “Just in case one of the students makes the same kind of connection,” he says.